Measurements and PR EoS Modeling of Thermophysical Properties at Vapor-Liquid Equilibrium Conditions for Natural Gas Condensate/Live Bitumen Mixtures.

In response to the need for less energy-intensive and greener bitumen recovery techniques, the use of multicomponent diluents through the expanding solvent steam-assisted gravity drainage (ES-SAGD) technique has garnered significant interest in recent years. In this work, we report new comprehensive measurements and Peng-Robinson equation of state (PR EoS) modeling of thermophysical properties (saturation pressure, density, viscosity, and K-values) of multicomponent mixtures of methane-bitumen-solvent. The multicomponent solvent is a natural gas condensate comprised of C3, i-C4, n-C4, i-C5, n-C5, C6, and C7+. Density, viscosity, solubility, and K-values of live bitumen (bitumen with dissolved methane) and various multicomponent mixtures are measured in the pressure range of 1-4 MPa and the temperature range of 313.41-459.10 K. A systematic approach is utilized to model the measured data. The experimental data show that the saturation pressure of the live bitumen can be controlled by selecting an appropriate solvent (condensate) composition. Condensate also has a significant effect on reducing the density and viscosity of the system. The results also show that the K-values of the components are almost independent of the composition of the solvent. The new comprehensive data set and the EoS model parameters reported in this work find applications in reservoir simulation as well as the design and optimization of the ES-SAGD process.

Asphaltene-Derived Graphene Quantum Dots for Controllable Coatings on Glass, Fabrics, and Aerogels.

Graphene quantum dots (GQDs) derived from natural asphaltene byproducts can produce controlled hydrophobic or hydrophilic interfaces on glass, fabrics, and aerogels. A set of facile solvent extraction methods were used to isolate and chemically prepare materials with different surface functionalities from a commercially derived asphaltene precursor. The organic-soluble fraction was used to create hydrophobic and water-repellent surfaces on glass and cotton fabrics. The GQD solutions could also penetrate the pores of a silica aerogel, rendering it hydrophobic. Alternatively, by extracting the more polar fraction of the GQDs and oxidizing their surfaces, we also demonstrate strongly hydrophilic coatings. This work shows that naturally abundant GQD-containing materials can produce interfaces with the desired wettability properties through a straightforward tuning of the solvent extraction procedure. Owing to their natural abundance, low toxicity, and strong fluorescence, asphaltene-derived GQDs could thus be applied, in bulk, toward a wide range of tunable surface coatings. This approach, moreover, uses an important large-scale hydrocarbon waste material, thereby offering a sustainable alternative to the disposal of asphaltene wastes.

Upscaling of dispersion in gas-liquid absorption on an inclined surface.

We extend the Taylor-Aris dispersion theory to upscale the gas absorption into a viscous incompressible liquid flowing along an inclined surface. A reduced-order model of advection-dispersion-reaction is developed with the aid of Reynolds decomposition and cross-sectional averaging techniques. The upscaled model allowed evaluation of the dispersion, advection, and absorption kinetics as a function of the Peclet number (Pe) and the Damköhler number (Da). The transport and kinetics parameters for the limiting cases of nonabsorption and absorption dominant are also evaluated. The upscaled model is solved analytically, and the obtained solution is used to evaluate the upscaled mass transfer between the gas and liquid. The results for the overall Sherwood number identify three regions: (i) advection dominant, (ii) transition where both advection and absorption play a role, and (iii) absorption dominant. The scaling relation between the Sherwood number (Sh) and the Da for the last region was determined to follow Sh∼Da^{1/2}. It is also revealed that in the first two regions, the Sherwood number versus the Peclet number exhibits a bell-shaped (or Gaussian) behavior, suggesting an optimal Pe that maximizes mass transfer between gas and liquid in these regions. The model and insights presented have the potential to be applied in a wide range of industrial separation processes involving the interaction of a gas exposed to a liquid flowing downward on an inclined surface under gravity.

Estimation of natural methane emissions from the largest oil sand deposits on earth.

Worldwide methane emission by various industrial sources is one of the important human concerns due to its serious climate and air-quality implications. This study investigates less-considered diffusive natural methane emissions from the world's largest oil sand deposits. An analytical model, considering the first-order methane degradation, in combination with Monte Carlo simulations, is used to quantitatively characterize diffusive methane emissions from Alberta's oil sands formations. The results show that the average diffusive methane emissions from Alberta's oil sands formations is 1.56 × 10-4 kg/m2/year at the 90th percentile of cumulative probability. The results also indicate an annual diffusive methane emissions rate of 0.857 ± 0.013 Million tons of CO2e/year (MtCO2e/year) from Alberta's oil sands formations. This finding suggests that natural diffusive leakages from the oil sands contribute an additional 1.659 ± 0.025 and 5.194 ± 0.079% to recent Canada's 2019 and Alberta's 2020 methane emission estimates from the upstream oil and gas sector, respectively. The developed model combined with Monte Carlo simulations can be used as a tool for assessing methane emissions and current inventories.

Gravity Drainage of Bitumen Induced by Solvent Leaching.

Steam-based thermal recovery processes are energy-intensive and pose environmental concerns due to their high greenhouse gas emissions. The application of solvents has shown promise in reducing the environmental impact of these processes. In this work, the solvent chamber theory is used to study the gravity drainage of bitumen. The results reveal that the drainage rate can be scaled using the thermophysical properties of solvents. The drainage rate is shown to be directly related to the density difference between bitumen and solvent and inversely proportional to the mixture viscosity. A universal scaling relation between the Sherwood number, as a measure of the mass transfer, and Rayleigh number, as a measure of the natural convection, in the form of Sh = ßRa is presented using the experimental data of various solvents. This linear relationship is consistent with the theoretical studies of buoyancy-driven convection. Moreover, the scaling prefactor ß is found to decrease with increasing natural log of the mobility ratio (α), which results in a lower rate of convective mass transfer. Furthermore, a new critical Rayleigh number equation based on the power-law mixing rule (PLMR) is derived, and the results are compared with the available theories in the literature based on the exponential mixing rule (EMR). The findings provide insights into understanding the convective dissolution with large viscosity contrast. Furthermore, the developed scaling relation provides a useful tool to predict the convective mixing of different bitumen/solvent systems. The results find application in the design of the solvent-based bitumen recovery processes.

Synthesis and properties of multi-functionalized graphene quantum dots with tunable photoluminescence and hydrophobicity from asphaltene and its oxidized and reduced derivatives.

Graphene quantum dots (GQDs) with tunable photoluminescence (PL) and hydrophobicity were synthesized from an abundant natural carbon source containing nitrogen, sulfur, and oxygen heteroatoms. Asphaltene and its oxidized and reduced derivatives were used as precursors to produce GQDs in organic solvents (i.e., methanol, toluene, and chloroform) using a facile ultrasonication technique. Asphaltene surface chemistry was tuned by sequential oxidation and reduction to investigate the surface effects on GQD properties. Spectroscopic characterizations confirmed the presence of N, S, and O heteroatoms and different electron-donating and electron-withdrawing groups. Microscopic characterizations revealed that these crystalline carbon nanomaterials have mono-layered or multi-layered structures with lateral sizes in the range of ∼5-15 nm. The asphaltene-derived GQDs exhibit tunable PL with emission colors ranging from blue to orange, depending on the carbon precursor and the organic solvent. Solvent exchange studies also revealed that asphaltene and its derivatives contain hydrophilic and hydrophobic fractions, resulting in varied hydrophobicity of the synthesized GQDs. Adding to the appeal of the present work, PL quenching of GQD-silica hybrid materials upon exposure to nitro-aromatics confirms that these GQDs can be incorporated to different host materials for advanced sensing or optoelectronic applications.

Dispersion tensor in stratified porous media.

Dispersion in porous media is of great importance in many areas of science and engineering. While dispersion in porous media has been generally well discussed in the literature, little work has been done regarding a generalization of Taylor dispersion in stratified media. In this work, we generalized the Taylor dispersion theory and Stokes flow in porous media to derive a reduced-order model for tracer dispersion in stratified porous media. Our findings revealed that for a simple case of two-layer porous media, the hydrodynamic coupling between the two layers leads to the tensorial nature of dispersion and advection. The results showed that the obtained dispersion tensor and advection are not symmetric unless both porous layers have similar thickness, porosity, and molecular diffusion. We found that the main elements of the coefficient of the dispersion tensor remain positive while the off-diagonal elements can take negative values. On the contrary, all elements of the advection matrix may take negative values. On the basis of these observations, we report the manifestation of the dispersion barrier, uphill dispersion and advection, and osmotic dispersion during tracer transport in stratified porous media. In particular, the identified uphill advection reveals that the injected tracer in one layer could be transported countercurrent to the adjacent layer. Furthermore, we have shown that in the limiting case of Darcy flow, the Taylor dispersion is absent, and the tracer mixing between the two layers is restricted to the cross-diffusive flux between them. The results revealed that the field scale mixing may not necessarily originate from the Taylor dispersion and could be due to the modified advection terms and the cross-diffusive flux between the two layers.

Standardized High-Performance Liquid Chromatography to Replace Conventional Methods for Determination of Saturate, Aromatic, Resin, and Asphaltene (SARA) Fractions.

One of the main approaches for compositional analysis of crude oils is SARA fractionation in which the sample is separated into saturate, aromatic, resin, and asphaltene fractions based on their polarity. A fully automated standardized SARA analysis for bitumen and heavy crudes has been developed and optimized using three commercial columns packed with different stationary phases based on the combination of adsorption and partition chromatography. The system is equipped with automated six-, eight-, and ten-port switching valves that control the flow direction. In this analytical technique, a bitumen (or heavy oil) sample diluted in toluene is swept through the column by pentane as the primary carrier phase. The sample is separated into four fractions by selective retention through interactions with the solvent mobile phases and the column stationary phases. The poly(tetrafluoroethylene) (PTFE) column filters asphaltenes, ZORBAX CN absorbs resins, and ZORBAX RX-SIL retains aromatics. Three samples of bitumen and heavy oils were fractionated to their SARA fractions by the developed method. Consistent results were obtained, proving the applicability of the new analytical technique to a wide range of crude oil samples. In addition, the performance of the developed SARA high-performance liquid chromatography (HPLC) method was compared with the conventional method, which demonstrates that it is more efficient, cost-effective, and consistent.

Bitumen Recovery Performance of SAGD and Butane- and Hexane-Aided SAGD in the Presence of Shale Barriers.

Oil and gas formations are commonly found to be heterogeneous, and one of the most common occurrences of reservoir heterogeneity is the presence of shale barriers. Shale barriers typically have very low permeability and high initial water saturation. Due to low permeability, these barriers obstruct the oil drainage path, specifically in thermal recovery methods such as steam-assisted gravity drainage (SAGD). In addition to flow assistance, they also lead to heat losses due to absorption by the high initial water saturation. Expanding solvent steam-assisted gravity drainage (ES-SAGD) is a hybrid technique comprising solvent co-injection along with steam. Solvent being in the vapor phase can potentially overcome the restricted path due to the presence of shale barriers. This paper presents a numerical simulation study on comparison between SAGD and ES-SAGD in the presence of shale barriers. SAGD and ES-SAGD with hexane and butane are numerically simulated for 240 lognormally generated shale realizations. First, both recovery processes are analyzed over the whole simulation period. Additionally, they have also been evaluated at multiple cumulative steam oil ratio cut-offs at 2, 2.5, 3, and 3.5. Transition points are defined and explained to cluster the shale density/fractions based on similar behaviors. It was shown that the oil that cannot be mobilized and produced by SAGD because shale barriers can be reached by the vaporized solvent through tortuous paths and recovered. Also, thermal losses are reduced because of lower steam chamber temperature. This led to efficient results for ES-SAGD over SAGD in heterogeneous formations.

Cost-effective and sensitive anthocyanin-based paper sensors for rapid ammonia detection in aqueous solutions.

In this work, we developed a cost-effective and environmentally friendly anthocyanin-based paper sensor with high sensitivity and optical visibility for the rapid detection of ammonia in aqueous solutions. The detection principle is based on a color change upon ammonia exposure to an anthocyanin-containing paper, which can be recorded simply via a smartphone. The paper sensors were fabricated by extracting anthocyanin from different sources (i.e., red cabbage, blueberry, and blackberry) and immersing pre-cut paper in anthocyanin extracts. Anthocyanin was extracted from different sources into water and aqueous ethanolic solution (80%) using solid-liquid extraction (SLE) and sonication assisted extraction (SAE) methods. The sensor sensitivity and optical visibility were improved by selecting a suitable combination of anthocyanin source, extraction technique, and solvent and controlling the ammonia release from the samples via alkalinization using a suitable base. Sensors fabricated with anthocyanin extracted from red cabbage (Red-C) into water using the SLE method and samples alkalinized with NaOH showed higher sensor sensitivity and better optical visibility. The Red-C anthocyanin sensors also exhibited a visible color change from dark to light blue for ammonia samples with concentrations as low as 2 mg NH3-N/L. Moreover, the spike recovery results of the sensors (101.9-109.4%) were in good agreement with those of the standard spectrophotometry method (105.4-112.2%), which suggest that these biosensors are a promising analytical tool as a replacement for time-consuming and environmentally unfriendly standard spectrophotometry methods for the on-site screening of ammonia.

A mesoscopic numerical study of shear flow effects on asphaltene self-assembly behavior in organic solvents.

A significant amount of research work has been conducted to shed light on the asphaltene aggregation behavior under no-flow conditions. However, their aggregation under shear flow conditions is poorly understood mainly due to the lack of research studies performed on this subject. In this work, we employ the Brownian dynamics simulation to examine the shear flow effects on the self-assembly behavior of asphaltenes. Three volume fractions φ of asphaltene nanoaggregates, ranging from 1 to 7%, are used to investigate the asphaltene aggregation behavior in heptane and heptol (i.e., a solvent containing both heptane and toluene) solvents under shear rates of [small gamma, Greek, dot above] = 0.0-2.5 × 108 s-1. The shear is applied parallel to the x-axis and the shear-gradient is along the y-axis. Under shear flow conditions, the formation of the percolating networks of aggregates is triggered at φ = 3% which is lower than that under the no-flow conditions, i.e., φ = 7%. In both solvent systems, the formed networks mainly percolate along the x- or z-axis to experience less shear-gradient. At all volume fractions, an increase in the shear rate from [small gamma, Greek, dot above] = 0.0 to [small gamma, Greek, dot above] = 2.5 × 108 s-1 resulted in two to three orders of magnitude improvement in the self-diffusion coefficients of colloids.

Efficiency of Urea Solutions in Enhanced Oil Recovery.

We examine the applicability of urea solutions as a novel cost-effective chemical for enhanced oil recovery processes. Two sandpack flooding experiments were conducted using 5 and 10 wt % urea solutions. Another flooding experiment was also carried out using the same sandpack with fresh water and used as a reference. Supporting experiments such as interfacial tension (IFT), viscosity of water in oil (W/O) emulsions, total acid number (TAN), and Fourier-transform infrared (FTIR) spectroscopy were conducted to confirm the generation of in situ surfactants by reacting urea solutions with the naphthenic acids in bitumen and evaluate their impact on the oil recovery. The analyses of FTIR, IFT, TAN, and viscosity measurements support the generation of in situ surfactants that leads to the formation of stable water in oil emulsions and hence a more stable displacement front resulting in higher oil recovery.

An Analytical Model for Estimation of the Self-Diffusion Coefficient and Adsorption Kinetics of Surfactants Using Dynamic Interfacial Tension Measurements.

We report a new analytical approach to model the transient diffusion and adsorption kinetics of a surfactant at a liquid/liquid interface using dynamic interfacial tension data. The developed model combined with the Frumkin/Langmuir isotherm is used to reproduce the experimental data of dynamic interfacial tension and predict the surfactant diffusion coefficient from a bulk solution to an interface and its adsorption kinetics. Experimental data of the dynamic interfacial tension of toluene and heptol solutions at various concentrations of asphaltenes (a natural surfactant) were employed to examine the ability of the developed model to regenerate the dynamic interfacial tension data. The model enabled us to estimate the apparent diffusion coefficient and adsorption kinetics of asphaltenes at different concentrations. The results showed that the diffusive migration of asphaltene toward an oil/water interface decreases at its higher concentrations and increases at higher concentrations of an aliphatic solvent such as n-heptane. Furthermore, the results reveal that the adsorption rate of asphaltenes at the interface increases at higher concentrations of surfactants and the aliphatic solvent. The developed analytical model finds applications in the prediction of the diffusion and adsorption kinetics of surfactants using dynamic interfacial tension data.

Development of Generalized Correlations for Thermophysical Properties of Light Hydrocarbon Solvents (C1-C5)/Bitumen Systems Using Genetic Programming.

Accurate modeling of thermophysical properties of solvent/bitumen mixtures is critical for proper design and implementation of thermal- and solvent-based bitumen recovery processes. In this study, three generalized correlations were developed for prediction of solubility, density, and viscosity of light hydrocarbon/bitumen mixtures. The generalized correlations were developed using symbolic regression based on genetic programming and employing a 10-year set of comprehensive phase behavior experimental studies conducted under the SHARP research program on solvent-aided thermal recovery of bitumen. The data set comprised Surmont, JACOS, Mackay River, and Cold Lake bitumen samples and five light hydrocarbon solvents including methane, ethane, propane, n-butane, and n-pentane. The developed correlations are valid for gaseous solvents. Finally, the developed correlations for solubility, density, and viscosity were validated against a large data set of experimental measurements collected from the literature. The validation demonstrates that the developed correlations are able to accurately predict the available experimental data of solubility, density, and viscosity reported in the literature.

Asphaltene Mesoscale Aggregation Behavior in Organic Solvents-A Brownian Dynamics Study.

Significant advances have been achieved in understanding the main molecular mechanisms leading to asphaltene aggregation. However, the existing computational deficiency of molecular dynamics simulations did not allow full reproduction of the complex aggregation behavior of asphaltene in the past. In this work, we use the Brownian dynamics simulation to investigate asphaltene aggregation behavior on larger length and time scales that have not been previously accessed by molecular simulations. This enabled us to completely render the formation of clusters of asphaltene nanoaggregates and the resulting fractal or network of aggregates during the aggregation process. Asphaltene aggregation is studied at several volume fractions (ϕ = 1-7%) of asphaltene nanoaggregates in two solvents including heptane and heptol (i.e., a mixture of heptane and toluene). Our simulation results support the aggregation hierarchy proposed in the Yen-Mullins model (Mullins, Annu. Rev. Anal. Chem. 2011, 4, 393-418.) by demonstrating that asphaltene nanoaggregates form small clusters with an aggregation number of 7-8 and an average gyration radius of ∼4.0 nm capable of forming either fractal aggregates with a fractal dimension of 1.93-2.04 at low ϕ or percolating networks of aggregates at high ϕ. Percolating structures are observed at ϕ = 7% in both solvents. In heptol, the structures mainly percolate along two directions, whereas in heptane, they can percolate along three directions (i.e., x, y, and z). The self-diffusion coefficient ( D) significantly decreases as ϕ increases. Generally, D is larger in heptol than in heptane, but this difference diminishes as ϕ increases, approaching to almost the same value at ϕ = 7%.

Onset of density-driven instabilities in fractured aquifers.

Linear stability analysis is conducted to study the onset of density-driven convection involved in solubility trapping of CO_{2} in fractured aquifers. The effect of physical properties of a fracture network on the stability of a diffusive boundary layer in a saturated fractured porous media is investigated using the dual porosity concept. Linear stability analysis results show that both fracture interporosity flow and fracture storativity play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in fractured porous media with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations for the onset of convective instability in fractured aquifers with single and variable matrix block size distribution. These findings improve our understanding of density-driven flow in fractured aquifers and are important in the estimation of potential storage capacity, risk assessment, and storage site characterization and screening.

Control of viscous fingering by nanoparticles.

A substantial viscosity increase by the addition of a low dose of nanoparticles to the base fluids can well influence the dynamics of viscous fingering. There is a lack of detailed theoretical studies that address the effect of the presence of nanoparticles on unstable miscible displacements. In this study, the impact of nonreactive nanoparticle presence on the stability and subsequent mixing of an originally unstable binary system is examined using linear stability analysis (LSA) and pseudospectral-based direct numerical simulations (DNS). We have parametrized the role of both nondepositing and depositing nanoparticles on the stability of miscible displacements using the developed static and dynamic parametric analyses. Our results show that nanoparticles have the potential to weaken the instabilities of an originally unstable system. Our LSA and DNS results also reveal that nondepositing nanoparticles can be used to fully stabilize an originally unstable front while depositing particles may act as temporary stabilizers whose influence diminishes in the course of time. In addition, we explain the existing inconsistencies concerning the effect of the nanoparticle diffusion coefficient on the dynamics of the system. This study provides a basis for further research on the application of nanoparticles for control of viscosity-driven instabilities.

Shear dispersion in a capillary tube with a porous wall.

An analytical expression is presented for the shear dispersion during solute transport in a coupled system comprised of a capillary tube and a porous medium. The dispersion coefficient is derived in a capillary tube with a porous wall by considering an accurate boundary condition, which is the continuity of concentration and mass flux, at the interface between the capillary tube and porous medium. A comparison of the obtained results with that in a non-coupled system identifies three regimes including: diffusion-dominated, transition, and advection-dominated. The results reveal that it is essential to include the exchange of solute between the capillary tube and porous medium in development of the shear dispersion coefficient for the last two regimes. The resulting equivalent transport equation revealed that due to mass transfer between the capillary tube and the porous medium, the dispersion coefficient is decreased while the effective velocity in the capillary tube increases. However, a larger effective advection term leads to faster breakthrough of a solute and enhances mass delivery to the porous medium as compared with the classical double-porosity model with a non-coupled dispersion coefficient. The obtained results also indicate that the finite porous medium gives faster breakthrough of a solute as compared with the infinite one. These results find applications in solute transport in porous capillaries and membranes.

Onset of dissolution-driven instabilities in fluids with nonmonotonic density profile.

Analog systems have recently been used in several experiments in the context of convective mixing of CO(2). We generalize the nonmonotonic density dependence of the growth of instabilities and provide a scaling relation for the onset of instability. The results of linear stability analysis and direct numerical simulations show that these fluids do not resemble the dynamics of CO(2)-water convective instabilities. A typical analog system, such as water-propylene glycol, is found to be less unstable than CO(2)-water. These results provide a basis for further research and proper selection of analog systems and are essential to the interpretation of experiments.

Characterization of scale-dependent dispersivity in fractured formations through a divergent flow tracer test.

Scale-dependency of dispersivity has been reported from field tracer tests. We present a simple methodology for characterization of dispersivity as a linear function of scale around an injection well using divergent flow tracer test data conducted in fractured formations. Results show that the slope of this linear dispersivity function can be estimated using tracer concentration measurements in a monitoring well. The characterized dispersivity function has applications in modeling of field-scale transport processes in fractured formations.